Design and characterization of micro-nano cellulose fibers composite separators for sodium-ion batteries

Cellulose fibers characterized by low cost, well chemical stability and environmental friendliness, are a significant direction for sodium-ion batteries separator materials . However, the cellulose film is dense due to the hydrogen bonding between hydroxyl groups, corresponding to the low porosity, ionic conductivity and poor wettability to the electrolyte of sodium-ion batteries, which seriously limits application performance. A strategy to regulate the microstructure of cellulose films using micro-nano cellulose fiber composites is proposed in this thesis. Micro-cellulose fibers are extracted from cattail rods and nano-cellulose fibers are obtained from ordinary qualitative filter paper, respectively. Cellulose-based composite separators are synthesized by a conventional screening method and the influence of composite ratios on the separator behaviors is explored. The composite separator with micro-nano fibers mass ratio of 2:1 has a better overall performance, including porosity of 88.3 % and ionic conductivity of 0.63 × 10 −3 S cm −1 . The assembled Na 3 V 2 (PO 4 ) 3 /Na half-cells deliver high cycle capacity retention rate of 97.0 % at 1 C after 500 cycles, rate capacity retention rate of 85.5 % at 10 C, as well as a small potential polarization and fine interface stability. These results provide alternative approach for the design of high-performance and low-cost cellulose-based separators for sodium-ion batteries. • The micron cellulose fibers with groove structure are extracted from cattail rod. • Composite separators are prepared by cattail microfibers and filter paper nanofibers. • Optimized composite separator shows excellent comprehensive performances.